It is known to provide a pneumatic tire casing with a fill to create a flat-proof assembly when fitted to a wheel of a vehicle. One common method is to assemble the tire and wheel and employ a valve to fill the cavity with a hardening material under pressure which when in place can be allowed to harden and create the fill. Once such material is urethane liquid accompanied by a hardening agent. Other polymers can be used and can be cured within the casing.
Urethane filled tires have a number of disadvantages associated therewith. Specifically, the known methods of filling urethane are performed while the tire casing is on the wheel and the curing and vulcanizing of the fill often requires a factory site. Further, urethane filled tires cannot be employed on vehicles which are to be driven at high speeds. This limitation is due to the fact that urethane tires when driven at high speeds experience heat build-up between the rubber tire casing and the urethane fill.
Furthermore, urethane is expensive and cannot be reused when the tire casing is worn out and subsequently discarded. Urethane filled tires provide a rough ride which is unacceptable to machine operators who must drive their vehicles during an entire working day. Further, filled tires have a high rolling resistance which contributes to the rough ride and results in high fuel consumption. Finally, filled tires are difficult to retread and due to the problem of casing stretching often become loose at the rim resulting in a loss of pressure.
Where solid vulcanized polymers other than urethane are used as tire fills, similar problems are encountered, especially reversion to liquid when used at high speeds resulting from the heat generated between the casing and the fill. The polymer in liquid form can leak from a loose rim or a cut or puncture in the tire casing. Low density foamed rubber is preferable, if it could maintain its strength at high speeds.
The best known of the presently used tire fill systems is the use of high density foam rubber as illustrated in U.K. Patent Application No. 2,164,903A. As is described in this patent, independent concentric rings of high density foam rubber are manufactured and installed in pneumatic tire casings. However, there are a number of disadvantages inherent in manufacturing and installing independent concentric rings in pneumatic tire casings. First, due to the vast number of different sizes and shapes of tires, it would be necessary for an installer to carry a huge inventory of rings. Further, the tooling required to produce the vast number of shapes and sizes of concentric rings is extremely expensive. Finally, forming the filler layers in concentric rings hinders their insertion into the pneumatic tire casing.